1. Field of the Invention
The present invention relates to a permanent magnetic rotor and a producing apparatus of the same, in particular, to a permanent magnetic rotor with fitting protrusions for pressuring and fixing permanent magnetic pieces in magnet insertion holes and a producing apparatus of the same.
2. Description of the Related Art
A permanent magnetic rotor which has a rotor iron core with blanked holes into which sector-shaped permanent magnet pieces are inserted is known. In this permanent magnetic rotor, the rotor iron core is made by layering a plurality of circular steel plates with blanked holes defined between two concentric circles at intervals of predetermined angles.
FIG. 29 is an exploded perspective view showing a conventional permanent magnetic rotor. In the figure, reference numeral 51 is a permanent magnetic rotor. The permanent magnetic rotor 51 comprises a rotor iron core 54, a plurality of permanent magnetic pieces 56, a pair of end plates 57, and a plurality of rivets 58. The rotor iron core 54 is made of a large number of steel plates 53 being layered. Each of the steel plates 53 has sector-shaped blanked holes 52. The blanked holes 52 of the steel plates 53 define magnet insertion holes 55. The permanent magnetic pieces 56 are inserted into the respective magnet insertion holes 55. The end plates 57 are disposed at both the ends of the rotor iron core 54. The end plates 57 are connected to the rotor iron core 54 by the rivets 58.
FIG. 30 is a cross sectional view showing the permanent magnetic rotor 51. In the figure, the steel plate 53 has a circular outer periphery. On the steel plate 53, the blanked holes 52 are defined between two concentric circles at intervals of approximately 90 degrees. The blanked holes 52 of the steel plates 53 being layered define the magnet insertion holes 55. An outer portion of the magnet insertion holes 55 of the rotor iron core 54 is an outer peripheral ring portion 59. An inner portion of the magnet insertion holes 55 of the rotor iron core 54 is a yoke portion 60. The outer peripheral ring portion 59 and the yoke portion 60 are connected by connect portions 61. In the magnet insertion holes 55, the respective permanent magnetic pieces 56 are inserted. The sectional shape of each permanent magnetic piece 56 nearly accords with the opening shape of each magnet insertion hole 55.
While the rotor is being rotated, each permanent magnetic piece 56 is exposed to centrifugal force and vibrations. To prevent the permanent magnetic piece 56 from vibrating, it must be fixed in the corresponding magnet insertion hole 55. However, the width of the outer peripheral ring portion 59 is preferably as narrow as possible so as to prevent magnetic flux from leaking. Thus, it is difficult to pressure and fix each permanent magnetic piece 56 in the corresponding magnet insertion hole 55 with large compression force due to the limitation of mechanical strength of the outer peripheral ring portion 59. In addition, it is also difficult to produce the permanent magnetic pieces 56 with high dimensional accuracy. Thus, the sectional shape of each permanent magnetic piece 56 does not accord with the opening shape of the corresponding magnet insertion hole 55 with high accuracy.
To solve this problem, in the conventional permanent magnetic rotor 51, a resin is injected between each permanent magnetic piece 56 and the corresponding magnet insertion hole 55 so as to fix the permanent magnetic piece 56. Alternatively, each permanent magnetic piece 56 is fixed by such a means as die-casting. As a result, the number of production steps of the permanent magnet rotor increases, thereby raising the production cost thereof.
To solve such a problem, however, a permanent magnetic rotor with protrusions has been proposed (as Japanese Patent Laid-Open Publication Serial No. SHO 63-80744). In the permanent magnetic rotor, protrusions are formed on the inner side of each magnet insertion hole. Each protrusion outwardly pressures a permanent magnetic piece so as to fix it.
FIG. 31 is an enlarged sectional view showing the permanent magnetic rotor disclosed in the Japanese Patent Laid-Open Publication Serial No. SHO 63-80744. In the figure, reference numeral 71 is a permanent magnetic rotor. The permanent magnetic rotor 71 comprises a rotor iron core 72 and permanent magnetic pieces 73. The rotor iron core 72 comprises a nearly cylinder-shaped yoke portion 74 and a narrow ring-shaped outer peripheral ring portion 75. Each permanent magnetic piece 73 is sector-shaped and disposed between the yoke portion 74 and the outer peripheral ring portion 75.
On the outer periphery of the yoke portion 74 of the permanent magnetic piece 73, a plurality of protrusions 76 which fix a permanent magnetic piece are formed. At a base portion of each protrusion 76, an opening 77 which creates an elastic force in the radial direction of the protrusion 76 is defined.
In the permanent magnetic rotor 71, the forward end of each protrusion 76 comes in contact with the inner side of the permanent magnetic piece 73. In addition, the forward end of the protrusion 76 is deformed by the compression force and the action of the opening 77. As the reaction, the permanent magnetic piece 73 is pressured toward the outer peripheral ring portion 75 by an elastic restoring force of the protrusion 76. Thus, the permanent magnetic piece 73 is fixed.
In the conventional permanent magnetic rotor with the protrusions, the opening defined at the base portion of each protrusion applies an elastic force to the protrusion. However, in this method, since the elastic coefficient in the radial direction of the protrusion is large, a large reaction tends to take place corresponding to a small compression displacement. Thus, the compression force of the protrusion is likely to break the permanent magnetic piece.
In addition, since the opening defined at the base portion of the protrusion is present at the yoke portion of the rotor iron core which is a passway of the magnetic flux of the permanent magnetic piece, it prevents the magnetic flux from flowing. Thus, the magnetic characteristics of the permanent magnetic piece are deteriorated.